PHYSIOLOGY OF THE LIVER AND SPLEEN. 821 



Experiments with subcutaneous injection of lactose gave similar 

 results, and it is generally believed that the liver cells cannot convert 

 the double sugars to glycogen, at least not readily; hence the value 

 of the hydrolysis of these sugars in the alimentary canal before 

 absorption. We may assume, therefore, that dextrose, levulose, and 

 galactose are the true glycogen-formers that occur normally in the 

 blood, and that the disaccharids (cane-sugar, milk-sugar, etc.) and 

 the polysaccharids (starches) are true glycogen-formers to the ex- 

 tent that they are converted into dextrose, levulose, or galactose. 

 Effect of Protein on Glycogen Formation. — In his first studies 

 upon glycogen Bernard asserted that it may be formed from protein 

 material. Since that time some doubt has been thrown on the 

 possibility of this transformation, but it may be said, perhaps, that 

 the trend of all recent work indicates that the amino-acids yielded 

 by proteins may serve as a starting-point for the formation of 

 glycogen. Direct evidence has been obtained for this latter state- 

 ment by feeding experiments with glycin, alanin, aspartic and glu- 

 tamic acid, prolin, serin, cystin, and arginin.* It may be assumed 

 that the amino-acids that undergo this change in the liver are first 

 deprived of their nitrogen by a process of deaminization and that 

 the non-nitrogenous organic acid remaining is synthesized to sugar. 

 From alanin, for example, by deaminization, lactic acid would be 

 produced — 



CH3CHNH2COOH + H2O = CH3CHOHCOOH + NH3, 

 and it is believed that the lactic acid can be synthesized to sugar — 



2C3H6O3 = CeHiaOe. 



The conclusion to be drawn from such experiments is strengthened 

 by clinical experience upon human beings suffering from diabetes. 

 In severe forms of this disease the carbohydrate material of the 

 food escapes oxidation in the body and is secreted unchanged in 

 the urine. If under these conditions the individual is given an 

 exclusively protein diet, sugar still continues to appear in the 

 urine, and it would seem that this sugar can only arise from the 

 protein food. In the similar condition of severe glycosuria that 

 may be produced by the use of phlorizin it has been shown that the 

 animal continues to excrete sugar even when fed on protein alone 

 or when starved. Under such conditions the amount of dextrose in 

 the urine bears a definite ratio to the amount of nitrogen excreted 

 D : N :: 3.65 : 1 (Lusk), which would indicate that both arise 

 from the breaking down of the protein molecule. So also the fact 

 that during prolonged starvation, lasting for forty or even ninety 



* Dakin, "Journal of Biological Chemistry," 14, 321, 1913. 



